The phrase Tom's assistant uses a single proper noun (Tom) with a possession or belonging (assistant). You have written it correctly.
Tom's assistant, a male secretary, graduated at the top of his class.
The businessman introduced us to Tom's assistant.
The correct placement for the apostrophe for "the boys" would be "the boys'."
No, the apostrophe in "it's" is incorrect. The correct form is "its" without an apostrophe, as "its" is the possessive form of "it."
No, "designers" does not have an apostrophe. The correct possessive form would be "designers'."
No, the correct spelling is "roof racks" without an apostrophe.
A possessive pronoun does not take an apostrophe. This is an exception to the rule that an apostrophe indicates the possessive. To write, 'the dog lost it's bone,' is not correct. The correct way is without the apostrophe: 'The dog lost its bone.' 'It's' (i.e., with an apostrophe) is correct only when used as a contraction of 'it is.'
learnings is spelled without an apostrophe just as in teachings.
No: the correct form is "it's hers". "Hers" does not have an apostrophe.
1925 is correct. There's no need for an apostrophe.
Apostrophe has only one name. It's apostrophe. The plural is apostrophes.
Unless it means "it is", there is no apostrophe in "its". See related question.
yes
The correct spelling is apostrophe.